The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines combust an air and fuel mixture within cylinders to drive pistons, which produces drive torque. Airflow into the engine is regulated via a throttle. More specifically, the throttle adjusts throttle area, which increases or decreases air flow into the engine. As the throttle area increases, the air flow into the engine increases. A fuel control system adjusts the rate at which fuel is injected to provide a desired air/fuel mixture to the cylinders. Increasing the air and fuel to the cylinders increases the torque output of the engine.
Engine control systems have been developed to control torque output by the engine to achieve a desired torque. Other vehicle systems, such as a chassis control system, may request that the torque output of the engine be increased above the driver requested torque for various reasons. For example, the excess torque may be used to eliminate dragging of a wheel of the vehicle, increase vehicle traction, increase vehicle stability, smooth a gear shift, and/or for other suitable purposes.
A wheel drag event occurs when a driven wheel of the vehicle decelerates at a different rate than undriven wheels of the vehicle. A drag event of a driven wheel may be caused by, for example, operation of the vehicle on a surface having a low coefficient of friction, a gear shift within a transmission, and/or deactivation of one more cylinders of the engine.
For example, the driver may remove pressure from the accelerator pedal (i.e., reduce the amount of torque requested from the engine) while the vehicle is on a surface having a low coefficient of friction. When the driver removes pressure from the accelerator pedal, vehicle losses cause a negative torque to be applied to the driven wheels of the vehicle. These losses may be attributable to mechanical losses (e.g., friction of the drivetrain), air losses (e.g., pumping losses of the engine), and/or other vehicular losses. As the coefficient of friction is low, the application of the negative torque will cause the driven wheels to decelerate at a faster rate than the undriven wheels and may cause the driven wheels to lock up.
Negative torques may also be applied to the driven wheels when various vehicle operations occur, such as when a gear shift from a lower gear ratio to a higher gear ratio is executed or when one or more cylinders of the engine are deactivated. The negative torque applied by shifting to the higher gear ratio may be caused by the mechanical linkage between the driven wheels and engaged gear. The negative torque applied by deactivating one or more cylinders may be caused by pumping losses of the engine and/or gas trapped within the deactivated cylinders.
When a drag event occurs, the chassis control system generates a drag torque request to increase the torque output of the engine above the driver requested torque. This torque is requested to accelerate the driven wheels to the speed of the undriven wheels. Increasing the torque output by the engine and accelerating the driven wheels when a drag event occurs increases vehicle stability and control.